Attractive and Repulsive Dipolar Interactions in Trilayer Transition Metal Dichalcogenides Open Access

Abstract

The study of atomically thin monolayer materials has given a unique insight into quantum many-body physics in the past decade, with potential applications in semiconductor devices and quantum information science. Transition metal dichalcogenides (TMDs) have been an area of particular focus in the field, due to their optical properties, which make them ideal photon emitters and detectors, and their lack of inversion symmetry which has opened up the new field of valleytronics [1]. Strong Coulomb interactions lead to excitons, which are tightly bound, optically generated electron-hole pairs that dominate the optical response of TMDs [2]. Interlayer excitons can form in certain TMD heterostructures, with the electron and hole occupying different layers. The resulting charge imbalance creates an electric dipole between layers [3]. Previous work has shown that the resulting dipolar interactions are strongly repulsive, as demonstrated by higher energy biexciton states with an energy increase of around 2 meV [4]. Here, we show that dipole-dipole interactions in TMDs can also be attractive when the dipoles are antiparallel, and by tuning exciton densities confined in moiré potentials we can induce shifts in energy up to 1.5 meV. These findings are a step towards understanding more complicated quantum many-body states that have been predicted for these systems, including exciton lattices and droplets [5, 6]. Furthermore, localized and finely tunable two-state quantum systems represent a major goal in quantum information science [7].

Table of Contents

1 Introduction 1

1.1 The band structure of TMDs . . . . . . . . . . . . . . . . . . . . . . . . . . 2

1.2 Excitons in TMDs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1.3 Repulsive dipolar interactions . . . . . . . . . . . . . . . . . . . . . . . . 9

1.4 Model for attractive dipolar interactions in trilayer TMDs . 11

2 Methods 15

2.1 Trilayer sample fabrication . . . . . . . . . . . . . . . . . . . . . . . . . . . 15

2.2 Photoluminescence Spectroscopy . . . . . . . . . . . . . . . . . . . . . . 17

2.3 Experimental Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

3 Results and Analysis 19

3.1 Characterization of anti-parallel dipolar excitons . . . . . . . . . 19

3.2 Power dependence of interlayer excitons . . . . . . . . . . . . . . . . .20

3.3 Effect of moiré potentials on exciton occupations . . . . . . . . . 27

4 Conclusions 31

5 Outlook 32

About this Honors Thesis

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School	Emory College
Department	Physics
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Physics, Quantum Physics, Low Temperature Physics, Condensed Matter
Keyword	Excitons Dipoles Transition metal dichalcogenides
Committee Chair / Thesis Advisor	Srivastava, Ajit, Emory University
Committee Members	Urazhdin, Sergei, Emory University Arnold, Dorian, Emory University

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